Be careful about these numbers: tíz, húsz, három, négy, hét. Három is a drop-vowel word! The rest becomes short when above 10: tizen, huszon, harminc, negyven, hetven. Be particularly careful about húsz because it becomes huszon with another number: huszonhét = twenty-seven. More examples:

Ketten voltak csak az állomáson.
There were only two people at the station.

Hatan támadták meg a fiatal lányt.Six people attacked the young girl.

Háromezren várták a bolt nyitását.Three thousand people were waiting for the opening of the shop.

Két millióan váltottak Internet szolgáltatót.Two million people have changed their Internet provider.

The other possibilities for száz, ezer and millió is the -NYI suffix or the TÖBB + -AN, -EN adverb. The -NYI suffix is different because it does not require the verb to be in the plural.

Több százan/ezren/millióan nem kaptak fizetést.Hundreds/Thousands/Millions of people didn’t get their paycheck.

Ezernyi/Milliónyi méh pusztult el a vegyszerek miatt.Thousands/Millions of bees have perished due to the chemicals.

Note that -nyi cannot be added to száz. No explanation. We don’t use it. It sounds kind of wierd.

2. They can take the POSSESSIVE SUFFIXES. The rules are the same: hét and tíz become short het- and tiz-. Három and ezer are drop-vowel words, so they become hárm-, ezr-. Kettő does not change in this case. With egy we’d rather use the subject + -nak, -nek instead of adding the possessive suffixes. The rest can take additionally the -nak, -nek suffixes if the verb requires them.

Egy gyermeknek nem adtak ebédet.
They didn’t give lunch to one child.

Kettőnk miatt ne maradj itt.
Don’t stay here because of the two of us.

Hármotoknak nem kell új személyi igazolvány.The three of you don’t need a new ID card.

Négyünk látta, hogy mi történt.The four of us saw what happened.

Always pay attention to how you translate a sentence. Many times Hungarian needs -nak, -nek, but English is transitive or reversed: hármotoknak nem kell – the three of you don’t need (literally: for the three of you it is not a must…)

3. They take the accusative case -T if necessary.

Tíz utas volt a buszon. Most csak hármat látok.
There were ten passengers on the bus. Now I can see only three of them.